The present invention relates to a hub for at least partially muscle-powered vehicles and in particular bicycles, the hub comprising a hub shell which is rotatably supported relative to a hub axle by way of two roller bearings disposed on opposite end regions of the hub shell. The hub comprises a rotor for non-rotatable arrangement of at least one sprocket, the rotor being rotatably supported relative to the hub axle by means of at least two rotor bearings. A freewheel device is provided between the rotor and the hub shell.
Other than in bicycles, the hub may be used in other partially muscle-powered vehicles and two-wheeled vehicles which are for example provided with an electric auxiliary drive. The hub is in particular used in sports bicycles.
The prior art has disclosed various hubs comprising a freewheel so that the pedal crank will not keep rotating along for example during a downhill ride. This freewheel also allows contrarotating of the hub shell and the rotor in backpedaling.
The prior art has disclosed hubs with ratchet freewheels where the pawls can radially pivot between a freewheel position and an engaging position. These hubs are provided with different numbers of ratchet pawls and tend to show four ratchet pawls symmetrically distributed over the circumference. As force is transmitted, the ratchet pawls engage a toothing in the rotor. The relatively low number of ratchet pawls results in a relatively large angle of rotation until rotational force is transmitted when pedalling is resumed.
GB 668,943 has disclosed a freewheel hub for bicycles showing screwed into the hub shell a shell-shaped part whose inside surface forms the raceway for the ball of the ball bearing, while a radially outwardly extending wall has an axial toothing formed thereat which together with an axial toothing forms an axial freewheel at the rotor. Due to the larger number of teeth of the axial toothing, re-engagement is faster as pedaling is resumed. The drawback of this system is that the rotor shifts in the axial direction when the hub is transferred to the freewheeling state and the engaged state. With the systems used today, this might cause a gear shift. Moreover, dirt and moisture might enter the freewheel and the hub interior, impeding or even entirely disabling the function which is dangerous to the rider.
DE 94 19 357 U1 has disclosed a hub with a toothed disk freewheel which reliably and very quickly transmits the driving force from the rotor to the hub shell while otherwise, friction losses are relatively low while the user does not activate the pedals. A toothed disk freewheel has many advantages and allows particular fast response of the freewheel. In this freewheel, a pair of toothed disks transmits forward rotational force of the rotor while in backpedaling, the teeth disengage axially. The known hub per se functions satisfactorily and is used in the area of sports and also in professional riding. However, there is the disadvantage that the high loads acting on the hub, for example in uphill rides may generate bending moments in the hub so as to cause the toothed disk to slightly tilt which results in higher wear on the teeth which are subjected to higher forces so that durability is limited and the toothed disks require early replacement to avoid malfunction.
DE 10 2010 033 268 A1 discloses a hub in which two end-toothed components form an axial freewheel. Pairs of adjacent hub bearings at the hub shell ends serve as supports relative to the hub axle. The drawback is the high space requirement for the adjacent hub bearings. Moreover, the hub axle is not provided with any radial shoulders so that it cannot serve for axially supporting the hub components. Therefore, to axially support the hub the axial force is transmitted from a roller bearing into the hub shell on one side and on the other side it is abducted through a roller bearing via sleeve elements disposed on the hub axle. In another embodiment, shown in a simplistic illustration one or two hub bearings are accommodated on the inside of the end-toothed component and in yet another embodiment shown in a simplistic illustration, an end toothing of the axial freewheel is integrally formed at the outer bearing race of the hub bearing so as to enable saving axial mounting space if only one hub bearing is used. The drawback is, however, that the axial forces must again be transmitted radially through the bearing into the hub shell. A freewheel must be configured for rotational forces of up to 400 Nm and higher. This means that in the course of operation, the end-toothed component screwed into the hub shell keeps being urged ever further into the hub shell so as to compress the hub shell. These high loads may result in the hub shell breaking or else the wall thicknesses require reinforcing which, however, increases the weight.
Also, hubs with toothed disk freewheels have been disclosed which are provided with a freewheel having an axial toothing, wherein an axial toothing is fixedly integrated in the rotor, and a toothed disk is non-rotatably and axially displaceably accommodated in the hub shell by means of one or more springs and is axially biased in the direction toward the toothing in the rotor. Reversely, a hub has been disclosed which includes a toothed disk freewheel and has a toothed disk fixedly integrated in the hub shell and where the other of the toothed disks is biased by means of a spring in the direction of the hub shell. Then again, both these hub types providing for axial movability of only one of the toothed disks have the disadvantage due to the high loads in sports or professional cycling that some of the teeth are subjected to higher loads and faster wear, so that early replacement on a regular basis is advisable of the toothed disks, the rotor or even the hub shell to avoid malfunction.
A feasible alternative would be a stiffer configuration overall of a hub with a toothed disk freewheel by employing stiffer and thus heavier materials or by employing greater wall thicknesses which would increase the weight though. However, since in sports and professional cycling each and every gram of weight counts, this does not provide the desired solution.
EP 1 121 255 B1 has disclosed a lightweight hub having a toothed disk freewheel and showing reliable function wherein the teeth of the toothed disks are stressed more evenly. This hub uses a pair of toothed disks, both of which are axially movable and are axially urged toward one another from the outside by means of a spring. The two toothed disks are thus floatingly supported and e.g. in case of the hub flexing or given other types of stresses they may show better positioning to one another, so as to provide more even wear on the toothed disks and a particularly reliable operation. However, an even stiffer hub is desirable.
Against the background of the prior art it is therefore the object of the present invention to provide a hub which is also lightweight or more lightweight still and which is perhaps even stiffer in configuration.